<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <ul class="message">
    <li>内容：</li>
  </ul>

  <input type="text" placeholder="请输入聊天内容" class="send">

  <script>
    const $ = s => document.querySelector(s)

    $('.send').addEventListener('keydown', e => {
      if (e.ctrlKey && e.keyCode === 13) {
        $('.message').innerHTML += `<li>${e.target.value}</li>`
        e.target.value = ''
      }
    }, false)
  </script>
</body>
</html>